Option for the NumberForm family giving the digits per block; the separators a full field would carry also widen a padded field
DigitBlock
NumberForm[30!, DigitBlock -> 3]
→ NumberForm[265252859812191058636308480000000, DigitBlock -> 3]NumberForm[N[10 ^ 5E], 15, DigitBlock -> 2]
→ NumberForm[271828.1828459045, 15, DigitBlock -> 2]NumberForm[N[10 ^ 5E], 15, DigitBlock -> {3, 2}]
→ NumberForm[271828.1828459045, 15, DigitBlock -> {3, 2}]