If you are outside IR35, you would typically take a small salary from your company which will allow you to benefit from statutory payments whilst minimising the amount of Employer’s and Employee’s National insurance and tax. The rest of the income you take from the company would be paid in the form of dividends which come out of the company’s post-tax profits.
The advantage of this is that dividends do not attract National Insurance and are taxed under the Corporation Tax regime.
If however you are caught by IR35 on an engagement then the majority of your income would be treated as “deemed salary” and subject to the same levels of taxation as a normal employee. There may still be some benefits of working via a limited company even if IR35 caught such as flat rate VAT and certain expense allowances but the financial advantages are less.
You can find more IR35 information here