If you don't pay the estimates and your withholding isn't any of the following you will be hit with underpayment penalties.
1) 2021 balance due after withholding is less than $1000
2) withholding covers 90% of 2020 tax
3) withholding is 100% (110% if 2021 adjusted gross income is over $150,000) of 2020 tax
See this for calculating 2020 estimated taxes - https://ttlc.intuit.com/community/tax-payments/help/can-turbotax-calculate-next-year-s-federal-estim...
See this for paying estimated taxes - https://ttlc.intuit.com/community/tax-payments/help/how-do-i-make-estimated-tax-payments/00/25875
