1) Unlimited Representation Rights allow a credentialed tax practitioner to represent you before the IRS on any tax matter. This is true no matter who prepared your return. Credentialed tax professionals who have unlimited representation rights include: Enrolled agents, Certified Public Accountants, and Attorneys.
2) Limited Representation Rights authorize a tax professional to represent you if, and only if, they prepared and signed your return. They can do this only before IRS Revenue Agents, customer service representatives and similar IRS employees. They cannot represent clients whose returns they did not prepare. They cannot represent clients regarding appeals or collection issues even if they did prepare the return in question. - LB
*See how to choose a tax return preparer wisely.