GM's Tip of the Week

To Prestige Class or not to Prestige Class
Well, that depends on the player, the campaign and how much hassle you might be willing to go through if it doesn’t work out. This, admittedly, is specific to systems that have Prestige Classes, or PrCs. If your group plays GURPS or any of the WW settings, or something else, you probably aren’t worrying about PrCs.

For the uninitiated, a PrC is a class with prerequisites that a player has to meet before they can take it. Common examples are the Arcane Archer, the Dragon Disciple, the Assassin, the Shadowdancer and the Dwarven Defender. Each edition that includes a PrC usually has something for everyone, and the list is actually a good deal longer than this. Pathfinder has such offerings as the Bloat Mage, the Magaambyan Arcanist, the Master Spy, and the Aldori Swordlord. I suspect 5e has a bunch specific to it, but I would be surprised if a variant on the Eldritch Knight wasn’t included.
Some things span editions; I believe there is a variant on the Shadowdancer in 3e, 3.5, Pathfinder, 4e and 5e. I wouldn’t be surprised at all to find some way to build one in 2e, now that I think on it. So, there are options, albeit they may not look exactly the same over the various editions.
My own experience generally suggests that cross-classing in general is a poor trade; you lose out on high-level bennies for your main class, and what you get in return is generally not worth what you lose. For a player planning to take a PrC, those trade offs should be known.
I recommend familiarizing yourself with the class regardless; the surprises are much more likely to come from abilities that don’t work as expected or intended – a common thread – or from powers that share names with more common spells, but do not work like those spells. Or feats.. there’s a long list. Some Pathfinder PrCs grant team work feats; sometimes this is useful, sometimes not, but definitely requires discussion with the rest of the group for what might be useful. Definitely check them for whether they can be granted to anyone in a specific range, or have to be taken by everybody to be useful; don’t just assume they are grantable.
I have seen PrCs used to great effect by savvy players and GMs; these classes should not be dismissed out of hand. Although, be aware that if your party’s wizard takes one that gives him access to Druid spells, you risk him being able to set up Reincarnation Contingencies. That specific example was a wizard that went for the Magaambyan Arcanist PrC. I don’t expect you will see many of those; but it did make for some very interesting moments (and allowed me to make a very powerful demonstration without risking the character in question too much). So, be aware.
In general, for the GM and the player, I highly recommend not skimming while reading up on a given PrC; even if it’s a class you are familiar with, new editions can change things up significantly, and little hidden things can make your game a good deal more interesting than you might have been expecting.