Well it depends on quite a few things. How early in the round is it? Am I an attacker or not? Randomness and unpredictability is essential always. Early game generally I'll have 5-30 lasers randomly placed on planets. Later in the round I'll check to see if it's a share. If it is a share and I'm a banker I won't build any more than a couple lasers since they will be able to full fleet. Otherwise I'll generally go with either 0, 30-80, or 400-600 lasers (as a banker on portalled planets). Obviously only a few planets should be laser trapped and people generally don't send more than 2k bombers to banker planets so there's not really a need to go over 1k lasers on any one laser trap to kill everything that's sent.

As an attacker it gets more complicated. In the early stages of a round you can put up 100 lasers to secure a key planet with a portal building when players don't have many bombers yet. After that, people will send much larger amounts of bombers to break your portals, especially since you will have a larger fleet than bankers so others won't risk sending large amounts of ground without large amounts of bombers. Sometimes it is right to laser trap in a shared system if you have a cancel nap that likely won't be broken for a while so lasers can slip through infils. If you laser trap a share it needs to be 3k+ lasers though since it will get hit with all their bombers. Otherwise, it depends on where on map the planets are. If it's a morale planet 2 ticks from your hs it doesn't need any lasers. Some planets towards the edge of the core will get ~1-2k lasers. If you don't go huge on lasers it's better to not have any at all since it just interferes with retakes and portals are usually sufficient to defend. I laser trap about ~10% of my planets when attacking.

Lasers are a nice surprise. If it's not a surprise it's useless, so putting 100 lasers on every planet isn't going to help you since they'll figure it out really quick from a couple PIs.

But who knows I may have made all of this up to throw people off when they attack me in the future

With classic morale formula, laser not effective anymore. I can build tons of bombers without worrying morale cost. Building too much laser just wasting my gc and iron, and if my enemy can break my port and take my infra, then i just pass those expensive lasers for free...
@sor laser is very usefull to stop someone raiding u, because income still low to build more bombers. When u already have good income, better use fighters trap than laser, coz laser trap need agents to prevent ur enemy to pi ur planet, means more gc for agents and higher upkeep+food consumed. Fighters trap is cheaper, can destroy enemy's fleet. Make them wasting more time to rebuild transports. Much2 better.

Also, I've been leader few times. I gave instructions on lasering planets. Some did not listen and became a victim of raid.

So, don't be a n00b and build lasers during SOR and early expo phase!

Plus, I really dont like capping 50 lasers per planet for everyone in family because it's only thing you can do to TRY defend but you need to build something else on it due to space issues. I think there should be two different kind of space, one for production buildings and one for defensive buildings so that way you really don't "cap" lasering level.  I like keep enemies guessing.

To be honest, ive been attacker almost all of my ic career (both active and inactive). It is so easy to take planets with lasers. All you have to do is build approximately 700 bombers per planet so you look at enemy on how many planets he has and do some random pis to find out what's their lasering levels are by average, then send fleets. You can probably just send 1k bombers per planet without needing for pis (which is risky, ofc)

When I asked a family to jump my bombers so big that I'll break family bank, they said no. I somehow convinced them to let me try it, they decided to let me try. I jumped enough bombers and took incoming explored planets nearby. Eventually, I was able to keep control of terriroty to keep enemies away by building portal and mass lasering. As a result, it was worth it. I even took a planet with 100-500 lasers, then build lasers on them SO enemy realized they cant afford bombers and decided to leave it alone. It happen sometimes. It's all about strategy.

But I think lasering at late game is not worth it as everyone will have enough bombers to do it.

Well, this tip is mainly for SOR attackers trying to gain position. While you are building portals on your planets in contested areas most decent fams will boost an attacker with a bunch of bombers to take it out if needed so a static amount of lasers isn't necessarily the best bet.

What I like to do is getting a decent amount of lasers to start with, then ideally making sure that every tick thereafter a new amount of lasers gets built. This way it's really hard to plan for opposing attackers how many bombers to get. The opposing attacker doesn't want to spend unecessary amounts of their fam bank on bombers seeing as minmaxing is really important at this point. This tactic of increasing every tick will either make sure the attacker mis-calculates his bomber amount or has to spend more than the minimum amount of bombers to take out your planet.

This of course only counts for offensive and very strategical positions where you know another family will try their damnest to take it.