All e-oligos oligos shorter than 40 mer do not require further purification if the applicaton is for PCR or sequencing.
A 20 mer oligo synthesized at a coupling efficiency of 99.5% will contain ~90% full length 20 mer and a mixture of truncated sequences of ~10%.
As the length of the oligo increases, even at a coupling efficiency of 99.5%, the yield of the full length oligo is reducing.
A 60 mer crude product will contain ~75% full-length oligo and similarly a 100 mer will contain ~60%.
Purification is strongly recommended for oligos longer than 50 mer.