Laptop covers just about everything. Master traits revolve around a particular build (especially now that MFa changed a bit) and limit your weapon choices, while providing you some rather powerful benefits that truly amplify the weapons they're made for.
The more powerful the advantage, the more limited your other options. Ammochain (MAc) is a perfect example: infinite bullets at the cost of inaccuracy (as it blocks Eagle Eye). This means you'll either be firing a lot or need to get your hands on some modifications. Army of the Dead (MAD) allows you to lay the hurt on any enemy, armored or not, but you lose Finesse and Hellrunner, two very useful traits. Fireangel (MFa), on the other hand, negates splash damage (useful defensively but not game-breaking) while giving you the chance to work on Fin->WK to mod your shotguns.
The safest master trait, at least for beginners, is Cateye. EE/SoB using rapid-fire weapons are ideal, and you're only one trait away from Intx2, a huge favorite for many players. If you're looking for a strategy that has the highest chance for success on the easier difficulties, look no further. (When things get harder, like N!, I've been leaning toward MFa in terms of master traits.)
A good example of choosing between a master trait or not is when deciding a pistol build. MGK is the only responsible master trait with pistols, but it blocks Son of a Bitch, preventing you from maximizing damage. As they are mutually exclusive, the choice is between MGK (a mid-range defensive build) and SoB (a long-range offensive build). Many of the other common builds are well-established in master traits, and there's little reason not to choose one when you're starting out.