Our Gemara on amud aleph considers that certain actions are not concrete benefits, and even if one made a vow to not receive any pleasure from the other person, he still may receive this kind of benefit.  For example, the Gemara considers paying a debt as metaphorically chasing away a lion, that is a non-act. Technically you didn’t give the person anything, you just saved his sheep from the lions. So too, paying a person’s debt might be considered just saving him from the creditor instead of giving him money. This idea of “chasing away a lion” also has literal applications for whether in certain situations the rescuer can demand payment or not for actually chasing away a lion (see Bava Kamma 58a and commentary.)

In any case, the Netziv (Ha’amek Davar Bereishis 15:1) applies this lomdus in a novel way to explain Avraham’s fear of having used up too much reward and Hashem’s answer.

By Avaraham it says (Bereishis 15:1):

אַחַ֣ר ׀ הַדְּבָרִ֣ים הָאֵ֗לֶּה הָיָ֤ה דְבַר ה֙ אֶל־אַבְרָ֔ם בַּֽמַּחֲזֶ֖ה לֵאמֹ֑ר אַל־תִּירָ֣א אַבְרָ֗ם אָנֹכִי֙ מָגֵ֣ן לָ֔ךְ שְׂכָרְךָ֖ הַרְבֵּ֥ה מְאֹֽד׃

Some time later, the word of Hashem came to Abram in a vision: “Fear not, Abram, I am a shield to you; Your reward shall be very great.”

The Midrash Rabbah (44:4) says Avraham’s fear was that he had been from the fiery furnace and from the Kings so he had used up all his reward.  Hashem reassures him that his reward though is still great. The Midrash uses the word “Magen” to connote shield, but it also means “free” in Aramaic.  Thus Hashem is saying that he gave all these protections for free, and thus it did not detract from his reward. The Netziv suggests that it is considered for free, because essentially God was merely chasing away Avraham’s attackers who started up with him (or Lot, but it still was their provocation, so it is considered Hashem chasing away an attack.)

Yet Yaakov is still afraid that his reward was used up too.  He states (ibid 32:11):

קָטֹ֜נְתִּי מִכֹּ֤ל הַחֲסָדִים֙ וּמִכָּל־הָ֣אֱמֶ֔ת אֲשֶׁ֥ר עָשִׂ֖יתָ אֶת־עַבְדֶּ֑ךָ כִּ֣י בְמַקְלִ֗י עָבַ֙רְתִּי֙ אֶת־הַיַּרְדֵּ֣ן הַזֶּ֔ה וְעַתָּ֥ה הָיִ֖יתִי לִשְׁנֵ֥י מַחֲנֽוֹת׃

I am unworthy of all the kindness that You have so steadfastly shown Your servant: with my staff alone I crossed this Jordan, and now I have become two camps. 

Rashi (Op. Cit.) says that Yaakov was specifically fearful that he has already used up his merits and will not be saved from Esav.  But why was Yaakov afraid, should he not have learned the “halakha” from Avraham, that this was merely fending off a damage instead of providing an actual benefit, and thus rightfully free of charge?

Ha’amek Davar suggests that Yaakov inserted himself into danger. He went to live by Lavan, and I would add, he demanded payment. He also ran away in the dark of night.  Therefore, he had less reason to consider his protections as merely preventing loss, but instead he had entered into a situation of imminent loss which is not considered the same (see Tosafos Bava Kama 58a “Iy Nami Mavriach Ari”).  I also will add, Yaakov engaged with Esau in a deceptive manner by the blessings, and even to an extent with Lavan in negotiating the payment terms and then using his theurgy to color the sheep (Bereishis 30:37-39. We can still argue that Yaakov was justified since Lavan was a trickster (and so says Bava Basra 123a), but it still was, all in all, a provocation.  So Yaakov had reason to worry that he used up his reward even though Avarah did not.