I did the same when I re-shingled my home built house around 16 years ago. I needed immediate protection after stripping the old shingles off. Being mostly a one man show putting the new shingles on, it took time to get it done. Also my roof pitch is low, at 3 in 12, another reason.I laid down 'ice and water shield' on 100% of my house addition back in 2014. while 'code' says only required for the first 3' (ice dam protection...), decided to protect the ENTIRE roof, cost was minimal compared to alternatives like 'tar paper' that WILL blow off during a bad rainstorm....
For my 24by24 garage the 'experts' said only 3 roof vents needed. I had to add 2 MORE,even then it's still dang HOT in the attic area. I also have 100% continuous soffit venting,something else 'they' said wasn't necessary(same cost BTW).
BUT that stuff is NOT cheap. Price is the disadvantage. Otherwise it is great stuff. I had a footprint of roughly 30x80, plus 2’ overhangs. Happy I spent the money though. Since that product has a sticky bottom, it performs as good as a finished roof until you get the shingles in place.