Is it advisable to maintain separate business accounts for various purposes ?

I have seen many businessmen have separate accounts for 

• GST/Non-GST Transactions
• 100% Cash Transactions

It's very difficult to keep records this way. separate accounts, separate balance sheets. Confusions might happen and much more.

Then why businesses do it ?

The major reason may be insecurity of loosing business. They feel that their business will go down if the do not do that. 

To me :- 

This is not true. There are many ( most of the good businessmen ) who will deal with you only if you have a GST number. When we do not enter any non-GST, transaction, these are filtered out. Same applies to Cash transactions. If we decide, as a policy, to do 100% white transactions, those not doing it will get filtered out & we shall just focus on 100% white transactions. Only the professionals who respect taxation.

Where is the question of insecurity ? Those who don't respect this, were never my customers.

This happens too much in the bottled water ( indian ) context. By the way, the tax rate is 18% ( GST ) in India.