The answer is: it depends.
Car-wise, it can be tricky to fit 3 car seats in, depending on what type you need.
When ds was due, I needed to be able to fit 1x hbb, 1x 5 point harness (can't remember - stage 1? the toddler one!) plus obviously a rear facing infant carrier. It proved tricky. And car seats have dictated the type of car I now have (ds is now 4) when I was due to change cars.
Holidays: again, it depends what type of holiday, and what budget you have. It can be tricky finding hotel rooms for 5, once the littlest is out of a cot. Interconnecting rooms can be similarly hard to come by. It is often more cost effective to hire a cottage or similar, but then you are self catering, which loses some of the holiday effect!
Mostly, it depends on age gaps, and how independent your older children are. It is only now stopping being a nightmare travelling (airports etc) for us, but then dd1 has severe ASD, so even at 12 is not at all independent, and needs more looking after/hand go,ding than 4 year old ds! At least now ds can manage stairs etc on his own, as it was tricky ensuring one hand on dd1 all the time, making sure dd2 was at least tagging along, and carrying ds as well, while H was left to sort out all the luggage...