It's still a trade-off, but it is now a lot more viable as a tactic than it was before.
There have been changes:
- The colony ship research has been moved down so that it is accessible at level 13 in the Academy, rather than at level 22.
- You can now build a colony ship at harbour level 10, rather than level 20.
These changes were relatively recent, although I can't remember the exact date.
Earlier access means that you now stand a good chance of being capable of colonising well before the end of Beginners' Protection (especially on worlds with longer protection, such as the 6 days for en103 Carystus). This means you can probably guarantee 2+ cities coming out of BP, and the 2nd city should be built up a bit as well. It is still the same trade-off of building up your own cities versus fighting the enemy for the chance to take a city that they have built up for you.
The ability to have a couple of decent colonisations being built up before the end of BP can be very beneficial for premade alliances, or for alliances that are able to organise themselves quickly. It allows a team to make a core, or to get isolated players into their core without the risk of losing the city before you are ready to colonise. The 12 hour window also helps, because it means that if you land a CS on an anchor before someone revolts the sending city, the colonisation is guaranteed to complete before you can lose the sending city (unless they used Helen).
The developers do seem keen to encourage more colonisation: en103 Carystus has a special setting that means that colonisations only take 12 hours, rather than 24 hours.