Any time something in the suspension is replaced or something adjustable is undone an a alignment is recommended.
While theoretically there are lots of little tricks to get the alignment close, it will never be perfect without verification with an alignment check. The biggest problem is that the replacement part is never exactly the same as the original especially if using after market parts.
If the threads in the tierod end are not cut exactly the same then it could be a quarter turn off and you'll never know. If the length of the threaded portion of the tierod is 1/8 of an inch longer then counting the threads is pointless.
There are magnetic angle gauges that can be used to realign a strut back, but again it's close but not prefect, same problem as the tierod.
What can be done without an alignment is a separation of the tapered part of a ball joint or a tierod. For example if the need to remove a CV axle arises there is not enough room to pull it out. Separate a ball joint and pull the knuckle out to give enough room to pull out the axle. After reassembly an alignment is not necessary.