The answer is simple: if you exceed the SPF 10 lookup limit, that is if you have too many mechanisms in your SPF record so as to exceed the SPF limit of 10 per SPF check, it will lead to SPF failure for your emails. This is because as soon as you exceed the SPF limit, your record is rendered invalid. This returns an SPF PermError result. To avoid this the recommended solution is to flatten (shorten) your record and remove redundancy using an SPF flattening tool like PowerSPF.
If you have DMARC implemented for your domains, the SPF permanent error is perceived by DMARC as an SPF failure. This can provoke the receiving server to prevent the email from reaching the recipient’s inbox. The only way to bypass this SPF limit is to keep your SPF DNS lookups restricted to a maximum of 10.
However, this isn’t as easy as it may appear. This is because if you’re running a business you would inevitably be outsourcing your email marketing campaigns, relaying messages via third-party vendors on a daily basis. If you don’t rely on SPF flattening, this will result in exceeding the SPF limit faster than you have anticipated and return SPF PermError results.