it is an option. usually not the cheapest one, but in quite a few cases makes more sense/convenience compared to flying - ie if you have less than 5-6 hour distance to cover it's faster, plus the hassle of airports, security, baggage limits, ending in the middle of nowhere compared to city centre etc are not that great.

another good thing is, you can buy in most cases tickets just days ahead, most trains have constant prices so your price isn't within 50-1000 eur boundary for same flight, same seat, depending on timing.