पितृपैतामहं नित्यं वश्यमद्वैध्यं महल्लघुसमुत्थमिति मित्रसम्पत् ॥ कZ_०६.१.१२ ॥
pitṛpaitāmahaṃ nityaṃ vaśyam advaidhyaṃ mahallaghusamuttham iti mitrasampat
The assets of an ally are these: an alliance inherited from the father and grandfather (long-standing), enduring, amenable to influence, not double-minded, and arising from either a great power or a minor power.
An ally is valuable when the relationship is long-standing, stable, influenceable, consistent (not double-minded), and can arise from either a major or minor power.
Because usefulness depends on reliability and alignment, not only size; even a smaller ally can be strategically significant if dependable and manageable.