There are two situations where that might be bad

Beginning of the fight: depending on your tank and how much better your gear is compared to them (or if they are just a bad tank at generating threat... happens sometimes) hitting your CD on your first Fire cycle might be too much damage too soon.

During very specific burn phases where you need as much DPS you can squeeze out. For example, Titan during the heart phase, Ifrit during the spikes, Garuda is just an all around burn this, burn that... so 2 of 3 primals have distinct burn phases. You pulling out 5 more dps because you always hit it on CD, verses causing a wipe because you didn't have that extra 20% damage during the burn phase... I would take the not wiping part

Otherwise, I wouldn't think it would be bad. I just have it easily within reach so I don't have a delay, rather than macro it together.