A very simple example:

Revenue: $ 1 000 All other cost except software: $ 500 Software cost: $ 100

Net profit (if software is allowed as opex): $400

Tax on $400 (@30%): $120

Net profit after tax: $280

However, if it is capex(amortized over 5 years):

Revenue: $ 1 000 Other cost (except software): $500 Software cost: $ 100

Net profit before tax: $ 400

Important: But now for tax purposes you can only deduct $20 this year as a cost ($100 amortized over 5 years)

So now you have to add back $80 to net profit for tax purposes: $480

Tax (@30%): $ 144

Net profit after tax: $400 - $144 = $256

So the difference is $280 - $256 = $24

Just a few notes:

1. I assume tax rate at 30%, it can be something else, principle stay the same

2. That all other expenses are tax deductible