Yes, you'd like to try to benefit from some of the run up, but the numbers of the dot-com boom are worth considering. The NASDAQ increase in 5 years preceding the crash was 600%, then the index lost 80% in the crash, so if you'd held through all of that you would have been left with 0.2 (100%-80%) x 7.0 (100% + 600%) of your original investment = 1.4 (140%), so you'd have been up 40% overall (OK for 5 years, but not amazing).

However, say you got onboard late and were "only" up 300% before the crash, then post-crash you'd have been left with 0.2 x 4.0 = 0.8 (80%), so you'd have ended up having lost 20% of your original investment, and of course the later you got onboard the worst off you'd have been.