It is fairly common for a couple making Lasting Powers of Attorney to appoint each other as their sole attorneys. It makes sense to let your spouse/partner make decisions on your behalf without someone else having to be involved.
For the most part this is absolutely fine, but there are circumstances where it can cause an issue. If both you and your spouse own property jointly together, and that property needs to be sold, then an attorney cannot sign both for both themselves as well as for the person they are acting as an attorney for. This is because owning a property jointly constitutes a trust of land and in order to sell that property, two (separate) trustees need to sign the transfer documents.
In reality, it is a situation that can be fixed fairly easily by appointing another trustee. However, this can not only be daunting, but will require legal advice. The easiest way to avoid the issue is to consider naming an additional attorney on your Lasting Power of Attorney. This would allow both attorneys to sign the transfer documents without the stress and expense of appointing another trustee.